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This study forms part of a suite of three technology studies from Pira focusing on chemical, water and energy recovery in pulp and paper making. With today's increasingly high energy and chemical costs and stringent environmental regulations, the need for improved recovery of chemicals from the pulp and paper making process has become a critical economic factor in the industry. It is essential that mills maximise steam and power production capacity, reduce recirculating chemical dead loads, and minimise chemical losses. This brand new study from Pira International takes a thorough look at the chemical recovery process and the scientific and technical advances right up to the very latest developments. It also discusses alternative chemical recovery processes, the utilisation of new value streams and environmental challenges.
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- Black liquor evaporation and combustion
- Current and alternative technologies for chemical recovery
- Current and future new value streams
Contents
Introduction
- Overview of chemical recovery
- Significance
- Scope and methodology
Black Liquor Evaporation
- Composition of black liquor
- Properties of black liquor
- Analysis of black liquor
- Black liquor evaporation
- Long-tube vertical evaporator
- Falling film evaporators
- Forced circulation evaporators
- Multiple effect evaporation
- Production of black liquor of high solids
- Other methods of concentration
- Vapour compression evaporation
- Blow heat evaporation
- Flash steam evaporation
- Scaling and scale control
- Evaporator trouble shooting
- Instrumentation and process control
Black Liquor Combustion
- Development of recovery boiler design
- Recovery boiler equipment
- Recovery boiler selection criteria
- Black liquor droplet combustion
- Recovery boiler operation
- Issues caused by non-process elements in the recovery cycle
- Safety aspects
- Modern recovery practices
- Future of recovery boiler technology
White Liquor Preperation
- Characteristics of the green and white liquors
- Slaking/Causticising chemistry
- Reactions in lime reburning
- Green liquor treatment
- Separation of dregs
- Cooling of green liquor
- Treating the dregs for proper disposal
- Recausticising
- Slaking and causticising
- White liquor clarification
- Lime mud washing and dewatering
- Automation and process control
Lime Reburning
- Lime kiln
- Lime kiln capacity constraint
- Fluidised bed calciner
- Flash calcining
Technologies for Chemical Recovery of Nonwood Black Liquor
- Desilication of green liquor
- Desilication of black liquor
- Soda recovery in the form of sodium carbonate without heat recovery
Direct Alkali Regeneration System (DARS) in Small Pulp Mills
Alternative Chemical Recovery Processes
- Black liquor gasification
- Gasification processes
- Environmental impact
- Unconventional causticisation technologies
- Partial borate autocausticisation
- Borate autocausticisation with black liquor gasification
New Value Streams (Fuels and Chemicals) from Residuals and Spent Pulping Liquors
- Removal of lignin from black liquor
- Future possibilities
- Removal of hemicellulose from black liquor
- Ethanol fermentation
- Biomass gasification
- Other products
Environmental Challenges